The present invention relates to fluid pressure devices, such as pumps and motors, and more particularly, to gear-type fluid pressure devices.
Although the present invention may be utilized with fluid pressure devices having various types of gear elements, it is especially advantageous when used with devices of the "external gear" type, and will be described in connection therewith.
Although the present invention may be used advantageously in connection with fluid pressure devices which are being utilized as motors, it is especially adapted for devices being used as pumps, and will be described in connection therewith.
A typical, prior art, external gear pump is illustrated and described in U.S. Pat. No. 3,713,759. The prior art external gear pump typically includes a pair of meshing, straight spur gears, each of the gears being fixed to its respective shaft. The forward end of each of the shafts is journalled within journal openings defined by a housing, while the rearward end of each of the shafts is journalled within journal openings defined by an endcap. Disposed between the housing and the endcap are the meshing gears, surrounded by another housing member. The two housings and the endcap are held in tight sealing engagement by a plurality of bolts.
In the prior art gear pump described above, it is essential that the journal openings within the housing and endcap which receive the opposite axial ends of the shafts be as nearly concentric (co-axial) as possible. Typically, in order to achieve such concentricity, a plurality of alignment pins (e.g., dowel pins) is received within bores defined by the housings and the endcap. As is well known to those skilled in the art, in order to achieve the objective of improved concentricity and alignment, the location and size of the pin bores relative to each other must be maintained very accurately. Furthermore, the size of the pin bores relative to the size of the pins must be machined within a very close tolerance. Such an arrangement adds substantial machining complexity and expense to the typical gear pump.
In the prior art arrangement described above, the fact that one end (rearward end) of each of the shafts extends into the endcap results in an endcap which is excessively thick in the axial direction, requires substantial machining, and becomes relatively heavy and expensive (in terms of both the amount of material and the machining required).
Another disadvantage of the prior art gear pump of the type described above is the extreme difficulty of making field conversions with regard to items such as the input shaft type, length, and diameter, and the direction of rotation of the pump. Also, it is not economically feasible with the conventional, commercially available gear pumps, to convert a standard (one pumping element) pump to a tandem plump by the addition of a second pumping section.